A disk changer adapted for CD or DVD disks generally includes a rotatable plate with several slots each for receiving a disk. The platter can be rotated on the chassis of the changer so that a desired disk can be moved to a playback unit optically reading the disk especially from the underside of the disk. Such an arrangement generally needs for proper operation two sensors. The first sensor generally in form of an optical sensor is adapted for sensing the number of a slot. Each slot carries some ribs of different number and size. Number and size of the ribs represent a code for the number of the respective slot. A sensor is provided on the chassis of the changer evaluating number and size of the ribs passing through the sensor during rotation of the platter. In this way each slot can be identified for feeding a disk to the playback unit the user wants to be reproduced. The second sensor is adapted to detect whether a disk is loaded in a given slot or not. This is useful, for example, to ignore or to skip a slot not containing a disk during a search operation by rotation of the platter in order to minimize the access time needed for finding a desired disk. Alternatively or additionally the second sensor can control a display unit showing which slot contains a disk and which slot does not contain a disk. The second sensor is not needed to be an optical sensor and may also be a mechanical sensor or whatever.
In fact, for both purposes several optical sensors and associated evaluation circuits are needed substantially increasing the total costs of the changer.